The present invention relates to a process for the production of ethylene oxide.
Ethylene oxide is used as a chemical intermediate, primarily for the production of ethylene glycols but also for the production of ethoxylates, ethanol-amines, solvents and glycol ethers. It is produced by the direct oxidation of ethylene with high-purity oxygen or air. Several processes for producing the ethylene starting material are known. For example, it is known to steam crack hydrocarbon streams, such as an ethane stream, a naphtha stream, a gasoil stream or a hydrowax stream, into ethylene. Further, it is known to produce ethylene by oxidative dehydrogenation (oxydehydrogenation; ODH) of ethane. Yet another way to produce ethylene is by conversion of an oxygenate, such as methanol, into ethylene.
All these ethylene production processes have in common that before any subsequent step wherein the ethylene is further converted into useful chemical intermediates, the ethylene containing product stream has to be purified. For example, the ethylene containing product stream has to be freed from ethane as the latter may interfere in any subsequent step, so that a purified ethylene stream can be fed to the subsequent step, such as the step of oxidation of ethylene. Said ethane may originate from the feed for producing the ethylene. For example, the above-mentioned ethane steam cracking and ethane oxydehydrogenation processes may result in product streams which still contain unconverted ethane in addition to the desired ethylene product. Further, such ethane may originate from ethylene production processes wherein ethane is produced as a by-product. For example, in the above-mentioned naphtha, gasoil or hydrowax steam cracking and methanol to ethylene conversion processes, ethane is produced as a by-product. Separating ethane from an ethylene product stream may be done by use of an ethylene/ethane splitter. Having to separate ethane from the ethylene is very cumbersome and results in a high expenditure for producing ethylene and results in relatively high ethylene losses.
Further, in case said purified ethylene stream not containing ethane is used to make ethylene oxide by oxidation, a ballast gas should be added. For in the oxidation of ethylene an oxidizing agent, such as high-purity oxygen or air, is required. In 1958, the direct ethylene oxidation process was modified by Shell to allow the use of high-purity oxygen, rather than air, as the oxidant. See: J. M. Kobe, W. E. Evans, R. L. June, and M. F. Lemanski, Encyclopedia of Catalysis, Istvan Horvath, Ed., Wiley-Interscience, v. 3, p. 246, 2003.
Because an oxidizing agent is required, it is important to control the safe operability of the reaction mixture. Historically, nitrogen was utilized as a ballast gas for the industrial epoxidation of ethylene. Over the past thirty years, the use of methane ballast has gradually replaced almost all commercial nitrogen-ballasted processes. One function of a ballast gas is thus to control this safe operability. Ballast gases that can be used in the production of ethylene oxide by oxidation of ethylene, are thus nitrogen and methane. It is very cumbersome to provide such ballast gas and feed it to the ethylene oxidation unit, which results in a high expenditure for producing ethylene oxide.
An object of the present invention is to provide a process for the production of ethylene oxide by producing ethylene and then producing ethylene oxide by oxidation of said ethylene, which process does not have the above drawbacks.